There are three approaches to producing hived bumble bees for use in pollination: (i) hiving natural colonies collected from the field; (ii) set- ting out artificial nest boxes to attract wild queens; and (iii) inducing bumble bees to nest year-round in captivity. The first two approaches appear simple but they give the grower minimum control over colony growth or synchrony with crop bloom; moreover, their success rate is poor. The third approach is labour intensive but lets one produce full- size bumble bee colonies at any time of the year; it represents the complete domestication of the bumble bee. Rearing bumble bees is labour intensive and fraught with variability. Nevertheless, a core of knowledge exists and the field is ripe for development.
Bumble Bees 67
Hiving colonies from the field
Bumble bee nests are not easy to find because they are usually located underground or in thick thatch. But if a natural colony is located it is possible to hive it using a few simple tools including a bee veil (see Appendix 1), gloves, a sheer insect-collecting net, one or more quart jars with lids, shovel, and some kind of hive for the colony. Any kind of weather-resistant box with a removable lid and small entrance hole can serve as a hive. The hive’s entrance must be temporarily closed with window screen or fine hardware cloth.
After one has donned protective clothing and before the nest is exposed it is possible to catch a large number of bees with a net as they fly to and from the entrance. Bees can be transferred from the net to a quart jar by scooping bees up in the jar as they walk up the sides of a net that has been inverted so that the opening faces down. After a while one can then begin excavating the nest, catching bees along the way. For nests near the surface, it is relatively easy to pull aside grass to expose the comb, carefully pick up the comb, and put it in the hive.
A shovel will be necessary for underground nests. Most bees have usually been caught by the time the comb is reached. After the comb has been transferred to the hive and all the bees are in the jar, the bees can be rapidly shaken into the hive and the lid quickly closed. The new hive should be relocated at least !smile (0.8 km) away to discour- age foragers from flying back to their original nest site. The temporary closure across the entrance can then be removed.
An alternative method is to transfer the comb and bees at night with the help of a red light (bees do not see red well). That way, one can capture more of the workers since most of them will be home for the night. They are also less likely to fly in the dark.
Relocated bumble bee colonies are stressed and one way to help them survive the ordeal is to temporarily provide them with food.
They can be fed sugar syrup (1 part sugar : 1 part water) or diluted honey in a gravity feeder that is inserted through the wall of the hive.
Berger et al. (1988) transferred field-caught and hived bumble bee nests to a field of male-sterile and male-fertile cotton in Texas.
They set out eight nests at ~50-ft (15 m) intervals along the 12 acre (5 ha) field. All colonies survived the transfer, resumed foraging, and continued rearing brood. Although only eight bumble bees were seen foraging on the cotton in 4 weeks of observation, up to 21% of the pollen reserves in the nests was cotton pollen. All colonies were parasitized with cuckoo bees by late August which seriously reduced the likelihood of the bumble bee colonies producing queens for the next season.
68 Chapter 8
Providing artificial nesting sites
The rationale for using artificial nest boxes is to increase local bumble bee populations by providing adequate nesting sites. This presup- poses that nesting sites are a limiting factor in the local habitat.
Queens become active and start seeking nest sites on warm days in spring when the first pollen sources begin to bloom. This is the time to set out artificial nest boxes.
Hobbs et al. (1960) and Hobbs (1967) attracted nesting queens in Alberta, Canada by setting out cubical plywood boxes roughly 6 in (15.2 cm) on all sides (Fig. 8.3). The plywood was #f in (1.9 cm) thick.
The entrance holes were %k in (1.6 cm) in diameter which permitted entry to bees but excluded mice. The boxes had hinged lids and were filled with upholsterers’ cotton which the bees used to line their nests. Boxes were fastened to posts with wire to keep skunks from turning them over. Hobbs (1967) favoured a ‘false underground’ nest, a regular nest box that is set on the ground but modified by using a 1-ft (30.5 cm) section of plastic pipe as an entrance tunnel (Fig. 8.4) and placing a piece of sod over the pipe in such a way as to leave pipe entrance exposed (Fig. 8.5). Presumably the sod gives the illusion that the pipe tunnel leads to an underground nest. Acceptance by queens was highest when the boxes were placed in fallow backyard gardens,
Bumble Bees 69
Fig. 8.3. An above-ground artificial bumble bee nest box after the design of Hobbs et al. (1960) and Hobbs (1967). The box is attached to the ground with a loop of heavy wire running through two eyelets and into the ground. (Source: Keith S.
Delaplane.)
70 Chapter 8
Fig. 8.5. The false-underground box is completed by covering the mid-section of the plastic pipe with soil or sod. This creates the illusion that the exposed end of the plastic pipe is leading to a subterranean cavity. (Source: Keith S. Delaplane.) Fig. 8.4. A false-underground bumble bee box after Hobbs (1967). It is similar to an above-ground box except for a section of plastic pipe leading from the
entrance. The lid is open to reveal the upholsterers’ cotton within. (Source: Keith S.
Delaplane.)
beside fence posts in a prairie, and along thickets of small aspen trees.
Bumble bee occupancy over 6 years averaged 44±23%. Macfarlane et al. (1983) achieved about 30–60% bee occupancy with a slightly dif- ferent box design in New Zealand. Occupancy of artificial nest boxes in Washington averaged only about 1% (D.F. Mayer, unpublished data), and occupancy in Georgia was zero after a two-season trial (K.S.
Delaplane, unpublished data). It seems that artificial nest boxes are most useful in areas where a shortage of natural nest sites is a limiting factor to bumble bee populations.
In order for bumble bee nest boxes to be useful for crop pollina- tion, it is important to set out boxes near the crop of interest or to relo- cate occupied boxes near to the crop. However, moving nests causes a loss of foragers (presumably because some spend the night in the field) and provokes queens to revert to foraging behaviour which increases the chance of their loss. Colonies that are moved produce fewer queens. Nevertheless, if one can achieve a reasonably good occupancy rate, then this practice may be able to increase bumble bee numbers at a crop. Relocating bumble bee boxes should be limited to crops that bloom relatively late in the season because this allows more time for colonies to recover an adequate foraging force.
One could conceivably increase the population of bumble bees in an area over time by repeatedly introducing bumble bee colonies which release new queens at season’s-end. With similar objectives, Clifford (1973) increased peak densities of local bumble bee popula- tions by importing and releasing 100 queens each spring for 3 years;
however, bee densities returned to their previous levels when queen importations stopped.
Rearing bumble bees year-round
The keys to rearing bumble bees year-round are: (i) inducing queens and males to mate in captivity; (ii) bypassing or abbreviating the queen’s natural diapause interval; (iii) inducing queens to rear a brood in captivity; (iv) growing colonies so that they produce a foraging force of workers; and (v) retaining some queens and males in order to start the cycle over again. A few companies rear bumble bees efficient- ly on a large commercial scale, but their methods are held as propri- etary secrets. Nevertheless, the scientific literature gives some information on bumble bee-keeping from which we made the follow- ing summary, supplemented by our own experiences (Plowright and Jay, 1966; Heinrich, 1979; Pomeroy and Plowright, 1980; Röseler, 1985;
Griffin et al., 1991; van den Eijnde et al., 1991; Tasei, 1994; Tasei and Aupinel, 1994; and S.A. Cameron, unpublished report). Different bumble bee species have different optimal rearing conditions, and some
Bumble Bees 71
simply take to domestication easier than others. Therefore, the follow- ing sections provide only a general guideline.
Honey bees as a source of pollen and surrogate workers
It is useful to have on hand one or two colonies of honey bees (see Chapter 6) with pollen traps (see Appendix 1). Honey bee hives thus fitted can provide fresh bee-collected pollen for feeding the bumble bees. Pollen must be collected daily from the trap and immediately frozen. It is important to collect and freeze enough pollen to sustain the operation during winter if it is intended to grow bumble bees year-round.
Young queens of the European bumble bee species Bombus ter- restriscan be stimulated to begin brooding when they are housed with young honey bees; in these cases, honey bee hives are necessary to provide these surrogate workers. Surrogate honey bee workers are apparently not helpful for rearing North American bumble bees.
72 Chapter 8
Fig. 8.6. A two-chamber queen starter box opened to reveal its components. A partition separates the chambers but has a passageway in order to allow bees to move between chambers. The chamber at the left is the feeding/defaecating chamber. There is a hole in the lid to accommodate a vial of syrup or honey water.
The floor is lined with disposable corrugated cardboard. A plastic lid on the floor catches drips. The nest chamber at right has upholsterers’ cotton and a plastic lid with a ball of pollen dough. A transparent Plexiglass inner cover allows the bee- keeper to inspect the nest chamber with minimal disturbance to the bees. (Source:
Nancy B. Evelyn.)
Surrogate honey bee workers should be used only when they are less than 12 h old. To harvest these young workers, one must open a honey bee hive and look for a comb of emerging worker bees. Combs of emerging bees contain a large quantity of capped brood and upon close examination one can see the ragged edges of recently-opened cells.
Light-coloured young bees (< 12 h old) will be walking on the comb, and one may see bees emerging from cells. When such a comb is iden- tified, it is brushed free of all adhering bees and placed inside a white plastic bag and stored overnight at comfortably warm temperatures.
The next morning there will be numerous young bees walking around in the bag. As long as the bag does not overheat and contains some honey from the comb, the bees can remain there until they are added to the bumble bee queen starter boxes within the next few hours.
The queen starter box
Queen starter boxes are small boxes in which mated queens are placed and induced to begin nesting. Reported dimensions are variable and probably do not matter greatly. One design is a box ~9 3 4.5 3 2 in (22.9 3 11.4 3 5 cm) with two chambers – a nest chamber and a feed- ing/defaecating chamber (Figs 8.6 and 8.7). This design keeps the box interiors dark, but the nest chamber can be easily opened and bees observed through the clear inner cover (light bothers some bumble bee species; others do not seem to object to it).
Bumble Bees 73
Fig. 8.7. An assembled two-chamber starter box. A piece of hardboard covers the Plexiglass inner cover of the nest chamber. (Source: Nancy B. Evelyn.)
The floor of the defaecating chamber can be made of small-mesh hardware cloth or be lined with a square of corrugated cardboard that is replaced as needed. In one design, there is no permanent floor in the defaecating chamber and instead a piece of cardboard or heavy blotting paper is taped to the bottom of the box and replaced as need- ed. Bees can pass between the nesting and defaecating chambers through a small circular opening. A defaecating area that is separate from the nesting area helps maintain general nest sanitation.
Some authors use single-chamber starter boxes. One such design is a ~4.75 3 2.25 3 4.25 in (12 3 5.5 3 11 cm) box with transparent Plexiglass side walls, and another is a ~4.5 3 1.75 3 1.75 in (11.3 3 4.5 3 4.3 cm) box with a Plexiglass lid.
Regardless of the design chosen, it is helpful to provide each box with a small plastic lid in the nest chamber on which pollen will be provided and the queen will build her brood clump. By encouraging the queen to nest on a plastic lid, it is a relatively simple matter to move the comb later when the incipient colony is graduating up to a finisher box. It is also helpful to attach a plastic honey bee queen grafting cup (see Appendix 1) to the floor of the plastic lid with melted beeswax; these cups simulate the shape and size of a natural bumble bee honey pot and may encourage nesting (Fig. 8.8).
A small wad of upholsterers’ cotton should be placed in the nest chamber; the queen will fashion the material into a fibrous shell
74 Chapter 8
Fig. 8.8.A plastic honey bee queen grafting cup (top left) simulates the size of a natural bumble bee honey pot and may encourage nesting. The brood clump (bottom right) has five brood cells that look like bulges off the central core of pollen.
Under each bulge are developing eggs or larvae. (Source: Keith S. Delaplane.)
around her comb. Some authors recommend chip foam (carpet padding) instead of upholsterers’ cotton. It is easier to handle and replace than upholsterers’ cotton. By cutting out holes in layers of chip foam, one can make a cavity for the pollen ball that is enclosed yet easily accessible (Fig. 8.9).
Some kind of gravity feeder for dispensing syrup or diluted honey should be inserted through the lid or wall of the feeding/defaecating chamber. The feeder can be a pipette with one end sealed off or a small inverted vial with a tiny perforation in its lid from which bees can drink. Another feeder design is a block of solid plastic with numerous feeding wells drilled into it. The wells are filled with syrup and the block placed in the feeding/defaecating chamber. Feeders should be cleaned at least after every third filling.
The finisher box
Queens that successfully rear brood in starter boxes must soon be transferred to larger finisher boxes in which the colony can grow to maturity. Conceivably, one could bypass the starter boxes but their failure rate is moderate to high and it makes sense to use small con- tainers that take up less space for that early precarious stage. Like starter boxes, published designs for finisher boxes are variable.
Outside dimensions for one design are ~11.75 3 8.25 3 6.75 in
Bumble Bees 75
Fig. 8.9. A nest chamber with chip foam (carpet padding) instead of upholsterers’
cotton. By cutting out holes in layers of chip foam, one can make a cavity for the pollen ball that is enclosed yet easily accessible. (Source: Nancy B. Evelyn.)
(30 3 21 3 17.5 cm). There are separate chambers, but this time the nesting chamber is larger than the feeding/defaecating chamber.
Ventilation is provided by holes drilled in the walls of the feeding/defaecating chamber and covered with hardware cloth (Fig.
8.10). Floors of the defaecating chamber can be made of metal mesh or lined with some kind of disposable absorbent material. The feeding/defaecating chamber must have a gravity syrup feeder.
It is ideal if the floor of the nest chamber is sloped upward, like an inverted cone, at angles of 35°. This design conforms to the natural shape of a growing bumble bee comb. One author achieves this effect by moulding nests of the correct shape out of porous concrete.
Another way to do this is to lay several layers of carpet padding inside the nest chamber. A hole is cut out of the centre of each layer of carpet padding, each hole successively larger than the one below (Fig. 8.11).
Ambient rearing conditions
It is important to provide favourable climate conditions for starter boxes and finisher boxes. Some authors maintain rearing rooms at
~82.4–86°F (28–30°C), 50–65% relative humidity, and in total dark- ness. Some light-sensitive species do better if the area is illuminated
76 Chapter 8
Fig. 8.10.A two-chamber finisher box designed to accommodate a queen and her growing colony. There are ventilation holes covered with hardware cloth in the side walls of the feeding/defaecating chamber and a flight entrance, closed in this photograph with hardware cloth and thumb tacks. (Source: Nancy B. Evelyn.)
with red light while the operator is feeding or inspecting the young colonies. Species that are not light sensitive do not need dark rearing rooms, but even with these species it is advisable to use boxes that are designed to keep interiors dark.
One option to humidifying the room is to humidify each starter box. One can do this by placing damp filter paper just under the lid of the nest chamber. This works best in finisher boxes provisioned with chip foam instead of upholsterers’ cotton (Fig. 8.12). The damp paper must be changed daily to avoid mould problems.
Feeding colonies in captivity
Fresh food must be prepared at the same time the incipient colonies are being started. A syrup made of 1 part sugar to 1 part water is pre- pared and placed in the gravity feeders. Some authors recommend putting the antibiotic Fumidil® B (see Appendix 1) in the syrup to control nosema disease. One option to sugar is a syrup made of 1 part honey to 1 part water. Honey syrup ferments more rapidly than sugar syrup and must be replaced more frequently (at least every 2 days), but bees can locate it more easily because of its attractive odour.
Fresh bee-collected pollen must be cleaned of visible debris, ground into a fine consistency, and added to sugar or honey syrup
Bumble Bees 77
Fig. 8.11. A finisher box opened to reveal the floor of the nest chamber. A hole is cut out of the centre of each layer of carpet padding, each hole successively larger than the one below, in order to create a cavity suitably-shaped for a growing brood comb. (Source: Nancy B. Evelyn.)
until it achieves a dry dough-like consistency. Pollen must be kept fresh-frozen in its bee-collected pellet form until it is needed. Queens produced from colonies that are fed fresh-frozen pollen are larger, have lower mortality rate, and produce larger colonies than do queens produced from colonies fed dried-frozen pollen (Ribeiro et al., 1996).
Catching queens and initiating nests
Queen bumble bees become active and fly on warm days in spring when early pollen sources become available. It is best to catch them while they are still searching for a nest site and have not yet started a nest; one can find such queens flying low to the ground in a zig-zag pattern obviously exhibiting searching behaviour. Queens with pollen on their legs have already started a nest in the field and are unlikely to resume nesting in captivity.
Queens can be caught with an insect net. They should be trans- ported individually in small jars padded inside with paper towelling and with lids loosened to provide ventilation and prevent over- heating. They should be transferred to starter boxes as quickly as pos- sible.
Bumble bee queens are placed individually in starter boxes. In the case of B. terrestris, each queen can be given three or four young honey bees as surrogate workers. A bean-sized lump of pollen dough
78 Chapter 8
Fig. 8.12. A damp filter paper just under the lid of the nest chamber is one way to humidify a starter box. It must be changed daily to avoid mould. (Source: Nancy B.
Evelyn.)